DESCRIPTION
REACTOR AND METHOD FOR CARRYING OUT A CHEMICAL REACTION
[0001] The invention relates to a reactor and a method 5 for carrying out a
chemical reaction according to the preambles of the independent claims.
PRIOR ART
10 [0002] In a number of processes in the chemical industry, reactors are used
in which one or more reactants are passed through heated reaction tubes
and catalytically or non-catalytically reacted there. The heating serves in
particular to overcome the activation energy required for the chemical
reaction that is taking place. The reaction can proceed as a whole
15 endothermically or, after overcoming the activation energy, exothermically.
The present invention relates in particular to strongly endothermic reactions.
[0003] Examples of such processes are steam cracking, various reforming
processes, in particular steam reforming, dry reforming (carbon dioxide
20 reforming), mixed reforming processes, processes for dehydrogenating
alkanes, and the like. In steam cracking, the reaction tubes are guided
through the reactor in the form of coils, which have at least one U-bend in the
reactor, whereas tubes running through the reactor without a U-bend are
typically used in steam reforming.
25
[0004] The invention is suitable for all such processes and designs of reaction
tubes. The articles "Ethylene," "Gas production," and "Propene" in Ullmann's
Encyclopedia of Industrial Chemistry, for example the publications dated April 15,
2009, DOI: 10.1002/14356007.a10_045.pub2, dated December 15, 2006, DOI:
30 10.1002/14356007.a12_169.pub2, and dated June 15, 2000, DOI:
10.1002/14356007.a22_211, are referred to here for purely illustrative purposes.
2
[0005] The reaction tubes of corresponding reactors are conventionally
heated using burners. In this case, the reaction tubes are routed through a
combustion chamber in which the burners are also arranged.
[0006] However, as described, for example, in DE 5 10 2015 004 121 A1
(likewise EP 3 075 704 A1), the demand for synthesis gas and hydrogen which
are produced with or without reduced local carbon dioxide emissions is, for
example, currently increasing. However, this demand cannot be met by
processes in which fired reactors are used due to the combustion of typically
10 fossil energy carriers. Other processes are ruled out, for example, due to high
costs. The same applies to the provision of olefins and/or other hydrocarbons
by steam cracking or dehydrogenation of alkanes. In such cases as well, there
is a desire for methods that emit lower amounts of carbon dioxide on site.
15 [0007] Against this background, the aforementioned DE 10 2015 004 121 A1
proposes an electrical heating of a reactor for steam reforming in addition to a
firing. In this case, one or more voltage sources that provide a three-phase
alternating voltage on three external conductors are, for example, used. Each
external conductor is connected to a reaction tube. A star circuit is formed in
20 which a star point is realized by a collector into which the pipelines open and to
which the reaction tubes are conductively connected. In this way, the collector
ideally remains potential-free. In relation to the vertical, the collector is arranged
below and outside the combustion chamber and preferably extends transversely
to the reactor tubes or along the horizontal. WO 2015/197181 A1 likewise
25 discloses a reactor whose reaction tubes are arranged in a star-point circuit.
[0008] In addition to the direct heating of reaction tubes, with which an electrical
current flows through the reaction tubes, there is also a wide variety of concepts
for the indirect electrical heating of reaction tubes. Indirect electrical heating can
30 take place, as described inter alia in WO 2020/002326 A1, in the form of external
electrical heating. Internal heating is also possible, as disclosed in WO
2019/228798 A1, for example. In addition to resistance or impedance heating,
3
inductive electrical heating of reaction tubes or of a catalyst bed, as described in
WO 2017/072057 A1, can take place. Inductive heating can, for example, heat an
internal or external heating element or the reaction tubes themselves. Direct (noninductive)
heating of a reaction tube is also disclosed in DE 10 2015 004 121 A1.
For heating, basic concepts with polyphase or single-phase alternating 5 current or
with direct current can be realized. In the case of direct heating of reactors by
means of direct current or also with single-phase alternating current, no star circuit
with a potential-free star point can be realized, but the power input can in principle
be realized in a similar manner as in the case of a polyphase direct current. The
10 present invention is suitable for all variants of electrical heating.
[0009] WO 2004/091773 A1 describes an electrically heated reactor for carrying
out gas reactions at high temperature. The reactor consists of a reactor block,
of one or more monolithic modules of a material suitable for electrical heating,
15 which modules are surrounded by a housing, of channels that extend through
the module(s) and are designed as reaction channels, and of a device for
conducting or inducing a current in the reactor block. The safety during operation
of such a reactor is to be increased in that the housing of the reactor block has
a double-walled jacket, which seals said reactor block in a gas-tight manner, and
20 at least one device for feeding an inerting gas into the double-walled jacket.
[0010] As also explained below, special safety-relevant aspects must be
observed in the case of electrically heated reactors. The object of the present
invention is to specify measures that take these aspects into account and in
25 this way allow advantageous operation of an electrically heated reactor.
DISCLOSURE OF THE INVENTION
[0011] Against this background, the present invention proposes a reactor and
30 a method for carrying out a chemical reaction according to the preambles of
the independent claims. Embodiments are the subject matter of the
dependent claims and the following description.
4
[0012] In an electrified furnace concept (the term "furnace" is commonly
understood to denote a corresponding reactor or at least its thermally insulated
reaction space) that is the basis of the present invention, reaction tubes, for
example, or corresponding tube sections thereof 5 (hereinafter also referred to
for short as "tubes") are themselves used as electrical resistors in order to
generate heat. This direct approach has the advantage of a greater efficiency
compared to indirect heating by external electric heating elements along with
a higher attainable heat flux density. However, as mentioned above, it is also
10 possible to carry out any other type of electrical heating (directly or indirectly,
as resistance, impedance, or induction heating, by means of a single-phase or
polyphase alternating current or with direct current) within the framework of the
present invention if said heating proves to be advantageous.
15 [0013] In the case of heating with polyphase alternating current, the power can
be fed into the directly heated reaction tubes via M separately connected phases.
The current-conducting reaction tubes connected to the M phases may also be
electrically connected to a star point at the other end. The number of phases M is
in particular 3, corresponding to the number of phases of conventional three20
phase current sources or networks. In principle, however, the present invention is
not restricted to the use of three phases but can also be used with a larger number
of phases, e.g., a number of phases of 4, 5, 6, 7, or 8. Thereby, a phase offset
amounts to in particular 360°/M, i.e., 120° for a three-phase current.
25 [0014] In electrical heating with polyphase alternating current, potential
equalization between the phases is achieved at the star point by the star
circuit, which ideally makes electrical insulation of the connected pipelines
superfluous. This represents a particular advantage of such a furnace
concept, since a break in the metallic reaction tubes for insulating certain
30 sections is undesirable, in particular because of the high temperatures used
and the high material and construction outlay thus required.
5
[0015] However, the measures proposed according to the invention and
explained below are suitable in the same way for the use of single-phase
alternating current and direct current, and the present invention can be used
both in reactors heated with alternating current and in reactors heated with
direct current or also in corresponding mixed forms. As 5 mentioned, the present
invention is also suitable for use in indirectly heated reaction tubes. In the case
of a direct current arrangement, only the type of the current source and the
region of the reaction tubes opposite to the power input or corresponding
sections supplied with current are, for example, different from an alternating
10 current arrangement. In the latter, an electrical connection of different tube
sections is only optionally carried out. Since a potential-free star point is not
present in a direct current arrangement, suitable current discharge elements
are to be provided, which safely conduct the current flow back to the outside.
The latter can be designed analogously to the power inputs described below.
15
[0016] The present invention relates to the protection of electrically heated
reactors of the type explained, which is necessary in particular in the case of
damage to the reaction tubes ("coil shredder"). In the case of corresponding
damage, one or more reaction tubes can, in particular, be severed
20 completely; however, the present invention is also advantageous for
leakages to a lesser extent. In the case of corresponding damage, a sudden
or creeping escape of combustible gas into the reactor vessel largely sealed
for reasons of thermal insulation occurs.
25 [0017] Such damage is a lower safety-related problem in conventional, fired
reactors than in purely electrically heated reactors, as are used in particular
according to the invention, since combustible gases emerging from the reaction
tubes in fired reactors, for example in the form of a hydrocarbon-steam mixture,
can be reacted immediately and continuously through the combustion taking
30 place in the reactor vessel or a corresponding combustion chamber, or since a
significantly reduced oxygen content is present due to the combustion taking
place and the gas space surrounding the reaction tubes is thus already
6
substantially "inertized." In contrast, in the case of purely electrical heating,
corresponding combustible gases could accumulate in the reactor vessel and
there, at the normal oxygen content of the air and temperatures above the
spontaneous ignition temperature, reach the explosion or detonation limit, for
example. In the case of combustion without explosion or detonation 5 as well, a
complete or incomplete combustion results in an energy input and thus possibly
overheating. Together with the gas volume flowing out of the reaction tubes, the
complete or incomplete combustion can per se in particular lead to a significant
pressure increase. The present invention reduces such a pressure increase
10 because combustion of the gas mixture is prevented.
[0018] In the terminology of the claims, the present invention relates to a reactor
for carrying out a chemical reaction, which has a reactor vessel (i.e., a thermally
insulated or at least partially insulated region), one or more reaction tubes and
15 means for the electrical heating of the one or more reaction tube(s). The reactor
proposed according to the invention is in particular set up to carry out a chemical
reaction at a temperature level explained below for high-temperature reactions.
The reaction tubes are guided through the reactor with at least one U-bend or run
through the reactor without any U-bends. The means for electrical heating can be
20 designed as explained extensively above. On the one hand, the means may be
means for feeding power into the one or more reaction tubes, which means bring
about a flow of current in the one or more reaction tubes and a corresponding
heating, for example rigid current rods guided into the reactor, but the means may
also be means for indirect heating, such as resistance and/or inductive heating
25 devices, which transfer heat conductively and/or by thermal radiation onto the one
or more reaction tubes, or which generate eddy currents, for example, in the one
or more reaction tubes or a catalyst bed and in this way bring about heating.
[0019] Within the framework of the present invention, the reactor vessel has one
30 or more discharge orifices, which are permanently open or are set up to open
above a preset pressure level, and gas feed means are provided, which are set
up to feed an inerting gas into an interior of the reactor vessel.
7
[0020] Below, a reactor is predominantly described that is designed according
to the invention or according to different embodiments of the invention. The
corresponding explanations also apply in each case to a corresponding
method, with which the correspondingly set up 5 means carry out the specified
method steps in each case.
[0021] For feeding the inerting gas, the gas feed means comprise, for example,
feed nozzles or openings that open into the reactor vessel, along with lines and a
10 gas reservoir connected thereto, whereby the inerting gas can be supplied to the
interior of the reactor vessel. The reactor vessel is in particular a chamber that is
predominantly, i.e., at least to 90, 95 or 99%, surrounded by a thermally insulating
wall. The interior of the reactor vessel is the region in which the reaction tubes are
arranged and which is surrounded by the reactor wall. A reactor wall that, for
15 example, can also be of double-walled design is not part of the interior.
[0022] In all embodiments of the present invention, the inerting gas can be a gas
or a gas mixture that has nitrogen, carbon dioxide and/or argon in a respectively
superatmospheric content, or the gas feed means are set up to provide a
20 corresponding inerting gas, for example by holding the corresponding inerting
gas available or by providing it by mixing pure gases or admixing pure gases to
air. In particular, the content of a non-combustible gas can be more than 50%,
60%, 70%, 80% or 90%. An inerting gas, therefore, does not have to be a pure
"inert gas" in the traditional sense; rather, it is sufficient if the inerting gas, in
25 particular due to its content of a non-combustible gas, at least partially reduces
the flammable range of the mixture, i.e., reduces the risk of ignition, explosion
or detonation. An inerting gas for use within the framework of the present
invention can in particular have a subatmospheric oxygen content, for example
an oxygen content of less than 10%, 5%, 1%, 0.5%, or 0.1%. An inerting gas
30 can in particular also be (completely or substantially) oxygen-free.
8
[0023] By means of the proposed measures, the present invention provides a
containment with a conditioned atmosphere, which containment serves for the
thermal insulation and for the safety-related protection of high-temperature
reactors, with which the energy input takes place electrically. Within the
framework of the present invention, a completely 5 electrical heating can in
particular be provided, i.e., the heating of the reaction tubes takes place, at
least within the reactor vessel, advantageously predominantly or exclusively
by thermal heating, i.e., at least 90, 95, or 99% of the amount of heat
introduced here, in particular of the entire amount of heat introduced here,
10 takes place by electrical heating means. A heat input via a gas mixture
conducted through the one or more reaction tubes remains disregarded here,
so that this proportion relates in particular to the heat transferred from the
outside to the wall of the one or more reaction tubes within the reactor vessel
or generated within the reactor vessel in the wall or a catalyst bed.
15
[0024] In its most general form, the invention thus describes a containment
for high-temperature reactors supplied with hydrocarbons (wherein the term
"high-temperature reaction" here refers in particular to a reaction that
proceeds at a temperature of more than 500°C and in particular of 700 to
20 1000°C) with electrical heating, which containment 1. provides an inerted
atmosphere in the surroundings of the tubes, and 2. is not permanently tightly
closed. The application for electrically heated reactors with which the process
gas temperature is close to or above the spontaneous ignition temperature
of the hydrocarbons contained in the process gas is particularly preferred.
25 The term "process gas" refers to a gas or gas mixture flowing through the
one or more reaction tubes.
[0025] Embodiments of the present invention differ in particular by the
embodiment of the one or more discharge orifices, which are permanently
30 open or are set up to open above a preset pressure level. However, a
combination of correspondingly designed discharge orifices is also possible
in principle.
9
[0026] In a group of embodiments referred to below as the "first group," the one
or more discharge orifices are permanently open. This means that the one or
more discharge orifices do not offer any mechanical resistance against the flow
of fluid into or out of the reactor vessel except for the possibly 5 existing narrowing
of the flow cross-section. The one or more openings are therefore not closed.
[0027] In contrast, in a group of embodiments referred to below as the "second
group," the one or more discharge orifices are set up to open above the
10 predetermined pressure level. The one or more discharge orifices are closed
below the preset pressure level or are set up to open temporarily or permanently
when the preset pressure level is reached. In this respect, the term "permanently"
open refers in particular to an irreversible opening, so that after subsequent
undershooting of the preset pressure level, no re-closure by discharging gas
15 takes place in this embodiment. In contrast, the term "temporarily" open refers to
an opening where re-closure does take place.
[0028] For opening at the preset pressure level, the one or more discharge
orifices may have, for example, one or more spring-loaded or weight-loaded
20 flaps, which have an opening resistance defined by the spring or load
characteristic values and therefore open only from a corresponding pressure.
In one embodiment of the second group of embodiments, one or more bursting
disks or pressure relief valves may also be used in a manner known per se. It
is also possible to detect a pressure value, for example by means of sensors,
25 and to trigger an opening mechanism of any type, for example an ignition
mechanism or an electrically actuated drive, when a preset threshold value is
exceeded. This makes it possible to release a sufficiently large cross-section,
which is kept closed in the explained manner during normal operation, within
a short response time when necessary.
30
[0029] In particular in the first group of embodiments, but possibly also in the
second group of embodiments, the reactor can be set up for constant purging
10
with inert gas. In other words, the gas feed means explained are set up to
continuously feed the inerting gas into the reactor vessel. In the first group of
embodiments, the inerting gas can flow out in particular predominantly through
the one or more permanently open discharge orifices, but optionally also
through further discharge orifices, in particular 5 unavoidable or deliberately
created gas leaks or bypasses, for example to an existing chimney. In the
second group of embodiments in which the one or more permanently open
discharge orifices are normally closed, further openings for the outflow of the
inerting gas are either provided, for example bypass lines to a chimney, or
10 inevitably present, for example due to leaks of the reactor vessel.
[0030] Alternatively to the constant purging, it may however also be provided to
supply the inerting gas only once or periodically to the reactor in accordance
with one or more predetermined criteria. The gas feed means are then set up
15 for such an operation. One or more predetermined criteria can include, for
example, reaching a preset pressure value and/or a preset concentration, for
example a minimum and tolerable oxygen content. However, one criterion may
also be that the reactor vessel is put into operation for the first time. In particular,
a continuous measurement can be carried out and the feeding of inerting gas
20 can be initiated whenever corresponding measured values indicate that the
preset criteria are no longer fulfilled. The one-time or periodic supply of inerting
gas can be provided, in particular in the second group of embodiments, below
the pressure value for the opening of the one or more discharge orifices since
free escape of the inerting gas can be prevented here and the inerting gas can
25 be held in the reactor vessel for longer periods of time.
[0031] In a particularly preferred embodiment of the first group of
embodiments, the reactor is set up for operation of the reactor vessel at a
subatmospheric pressure level. In this case, means for forming a gas flow out
30 of the reactor are provided. In this connection, the one or more discharge
orifices, which, in this group of embodiments, are permanently open after all,
can be connected permanently open to a chimney that has a chimney mouth
11
at a sufficient height. This results in a static negative pressure in the reactor
vessel due to the high temperatures in the reactor vessel and the resulting
lower density of the gas volume contained. In this connection, it is also possible
to provide the use of blowers, for example, up to the formation of a
corresponding 5 static negative pressure.
[0032] In contrast, in a particularly preferred embodiment of the second group
of embodiments, the reactor is set up for operation of the reactor vessel at a
superatmospheric pressure level. This can be achieved in particular by
10 feeding the inerting gas up to a superatmospheric pressure level, which is
below an opening pressure of the discharge orifices.
[0033] The system according to the first group of embodiments, which has been
inertized up to a certain degree and is "open" to the environment (in particular
15 with a slight negative pressure in the reactor vessel as a result of the chimney
effect) or else the "openable" system according to the second group of
embodiments of the present invention (which can be operated in particular with a
certain overpressure in the reactor vessel) can limit the pressure increase rate, in
the case of an escape of hydrocarbons damage to the reaction tubes, to a
20 tolerable amount that satisfies the design limits of the reactor vessel.
[0034] The oxygen content present there can be reduced as a result of the
concept of a reactor vessel supplied with inerting gas. The reaction rate of the
hydrocarbons escaping in the event of damage and thus the significant
25 additional volume increase (as a result of the reaction heat input) scales in a
first approximation with the oxygen partial pressure or the molar oxygen
content in the box.
[0035] In both groups of embodiments of the present invention, as a result of the
30 feeding of the inerting gas, the walls of the reactor vessels advantageously do not
have to be designed to be completely gas-tight, which could only be carried out
with very high material outlay, for example the use of temperature-resistant
12
bellows structures and the like, due to the high temperatures at certain locations
due to a required possibility of movement. In the case of operation at the
subatmospheric pressure level in conjunction with a chimney, although air can
possibly be drawn into the reactor vessel via corresponding leaks, this air is
discharged and diluted accordingly by the continuous flow brought 5 about by the
chimney. Safety problems in the use of inerting gases that potentially impair
breathing or of components thereof can be prevented in this way. In contrast, in
the case of operation at a superatmospheric pressure level, an inflow of air into
the reactor vessel can be reliably prevented due to the uniform pressure
10 propagation. Inerting gas escaping via leaks can be discharged or diluted, for
example, by sufficient ventilation outside the reactor vessel.
[0036] As a result of the proposed concept of the reactor vessel supplied with
inerting gas, the oxygen content can be reduced here. As can be utilized
15 according to the invention, the reaction rate of the escaping hydrocarbons
and thus the significant additional volume increase rate (as a consequence
of the reaction heat input) correlates in a first approximation with the oxygen
partial pressure or the oxygen mole fraction. This correlation is summarized
in Table 1 below, wherein xO2 denotes the molar oxygen content and Vreak
20 the reaction-related volume increase rate.
[0037] The gas feed means are therefore advantageously set up to adjust a
maximum oxygen content in the reaction vessel on the basis of a
dimensioning of the chimney or the chimneys.
25
Table 1
xO2
[vol.%]
Vreak
[m3/s]
21 218
15 156
13
10 104
5 52
3 31
1 10
0.1 (almost inert) 1
[0038] The maximum permissible pressure pmax follows from the mechanical
stability of the respective chambers or a surrounding containment. This
pressure must be at least as large as the pressure pbox in the case of a coil
shredder or in the case of a corresponding other 5 safety-relevant event, which
in turn depends on the volume VBox of the relevant chambers, on the chimney
diameter DChimney and the molar oxygen content:
pmax ≥ pbox = f (VBOX, DChimney, xO2)
10
[0039] This requirement results in a design basis for the dimensioning of the
chimney, that is to say the connection to the environment, which is
permanently or temporarily present via the one or more discharge orifices,
and vice versa. This relationship is now explained once again with reference
15 to Figure 9. If, for example, a maximum permissible pressure increase of 20
mbar is used as a basis here, as illustrated by the dashed lines 601 and 602,
in order to be able to use a chimney with a diameter of 500 mm (dashed line
601), a reaction-related volume increase rate of at most approximately 10
m3/s may result, which leads to a maximum oxygen content of approximately
20 1%, which is adjusted by the inertization.
[0040] Conversely, if an inertization to an oxygen content of at most 1% is to
be carried out, a chimney diameter of at least 500 mm must thus be used. In
order to be able to use a chimney with a diameter of 900 mm (dashed line
25 602), only a volume increase rate of approximately 42 m3/s may result, which
leads to a maximum oxygen content of approximately 4%, which is adjusted
14
by the inertization. Conversely, and analogously to the explanations above,
if an inertization to an oxygen content of at most 4% is to take place, a
chimney diameter of at least 900 mm must be used here.
[0041] The smaller the oxygen content in the reactor vessel, 5 the smaller is
the volume increase. Consequently, the diameter of the emergency chimney
that must discharge the additional volume can also be smaller. Important for
an efficient limitation of the oxygen content is always sufficiently good sealing
with respect to the environment, in order to prevent the entry of oxygen10
containing false air as far as possible or in a sufficient manner. As explained,
however, complete sealing is not required.
[0042] In other words, within the framework of the present invention, a
maximum oxygen content in the reaction vessel is thus adjusted by means
15 of the inerting gas, which maximum oxygen content is selected in the first
group of embodiments in the presence of a chimney on the basis of a
dimensioning of the chimney or the chimneys, or the gas feed means are set
up for feeding inerting gas or for adjusting the oxygen content on this basis.
The gas feed means can also be set up in particular to feed in such a way
20 that a target pressure is not exceeded. In the second group of embodiments,
it is likewise possible for feeding to take place on the basis of an oxygen
concentration or a target pressure and chimney dimensioning.
[0043] An amount of the inerting gas fed in can be regulated by corresponding
25 regulating means, in particular on the basis of an oxygen measurement in the
reactor vessel or in the chimney, if present, as a result of which the oxygen
content can be kept constant during operation. A corresponding safety concept
comprises according to the invention that operation of the reactor is or
continues to be prevented when the measured oxygen content exceeds a
30 target oxygen content. For example, a feeding of hydrocarbons into the
reaction tubes and/or the heating thereof can be released only when a required
15
oxygen content is undershot. When a fault is detected, reaction operation with
hydrocarbon addition into the reaction tubes can be prevented in general.
[0044] An impermissible escape of gas from the reaction tubes can be
detected, for example, via pressure measuring sensors, 5 wherein a feeding of
hydrocarbons into the reaction tubes can be prevented when gas escape is
detected in order to minimize the total amount of escaping hydrocarbons.
[0045] For detecting very small damage (leakage flow without drastic
10 pressure increase), the hydrocarbon content in the reactor vessel or the
chimney, if present (for example in the form of a carbon monoxide
equivalent), can also be measured continuously. An impermissible value can
likewise result in the prevention of the hydrocarbon feed.
15 [0046] The present invention therefore encompasses, more generally
speaking, that a value that characterizes a gas escape from the one or more
reaction tubes is determined on the basis of a pressure and/or hydrocarbon
measurement, and that one or more safety measures are initiated if the value
exceeds a preset threshold value.
20
[0047] With the method proposed according to the invention for carrying out a
chemical reaction, a reactor is used which has a reactor vessel, one or more
reaction tubes, and means for the electrical heating of the one or more reaction
tubes. According to the invention, the reactor vessel used is a reactor vessel that
25 has one or more discharge orifices, which are permanently open or are set up to
open above a preset pressure level, and an inerting gas is fed according to the
invention into an interior of the reactor vessel by using gas feed means.
[0048] For further features and advantages of a corresponding method, in which
30 a reactor according to one of the previously explained developments of the
invention is advantageously used, reference is made to the above explanations.
16
[0049] The invention will be further elucidated below with reference to the
accompanying drawings, which illustrate developments of the present
invention with reference to and in comparison with the prior art.
5 DESCRIPTION OF THE FIGURES
[0050] Figure 1 schematically illustrates a reactor for carrying out a chemical
reaction according to a non-inventive development.
10 [0051] Figures 2 to 8 schematically illustrate reactors for carrying out a
chemical reaction according to an embodiment of the invention.
[0052] Figure 9 schematically illustrates principles of dimensioning a chimney
according to an embodiment of the present invention.
15
[0053] In the following figures, elements that correspond to one another
functionally or structurally are indicated by identical reference symbols and for
the sake of clarity are not repeatedly explained. If components of devices are
explained below, the corresponding explanations will in each case also relate
20 to the methods carried out therewith and vice versa. The description of the
figures repeatedly refers to alternating current heating. As mentioned,
however, the present invention is also suitable in the same way for the use of
direct current for heating. Reference is made here to the above explanations.
25 [0054] Figure 1 schematically illustrates a reactor for carrying out a chemical
reaction according to a non-inventive development.
[0055] The reactor here designated 300 is set up to carry out a chemical
reaction. For this purpose, it has in particular a thermally insulated reactor vessel
30 10 and a reaction tube 20, wherein a number of tube sections of the reaction
tube 20, which are designated here by 21 only in two cases, run respectively
between a first zone 11' and a second zone 12' in the reactor vessel 10. The
17
reaction tube 20, which will be explained in more detail below with reference to
Figure 2, is attached to a ceiling of the reactor vessel or to a support structure
by means of suitable suspensions 13. In a lower region, the reactor vessel can
in particular have a furnace (not illustrated). It goes without saying that a plurality
of reaction tubes can be provided in each case here 5 and subsequently.
[0056] Figure 2 schematically illustrates a reactor, which is overall denoted
by 100, for carrying out a chemical reaction according to an embodiment of
the present invention.
10
[0057] The zones previously denoted by 11' and 12' here take the form of
regions 11 and 12, wherein the tube sections 21 for heating the tube sections
21 in the first regions 11 can in each case be electrically connected to the
phase connections U, V, W of a polyphase alternating current source 41 via
15 connection elements 42, as a result of which means denoted as a whole by
40 for electrically heating the reaction tube 20 are formed. Switches and the
like as well as the specific type of connection are not illustrated. In the
embodiment of the invention illustrated here, the tube sections 21 are
electrically conductively connected to one another in the second regions 12
20 by means of a connecting element 30, which is integrally connected to the
one or more reaction tubes 20 and is arranged within the reactor vessel 10.
A neutral conductor can also be connected to the connecting element 30.
[0058] In the example illustrated here, a star circuit of a plurality of alternating
25 current phases is thus realized. As mentioned several times, the invention
can however also be provided using single-phase alternating current heating,
direct current heating, or other means for heating, for example for inductive
or indirect heating in the sense explained above.
30 [0059] In the reactor 100 illustrated here, a plurality of tube sections 21 of one
reaction tube 20 (although a plurality of such reaction tubes 20 may be
provided) are thus arranged side by side in the reactor vessel 10. The tube
18
sections 21 pass into one another via U-bends 23 (only partially denoted)
and are connected to a feed section 24 and an extraction section 25.
[0060] A first group of the U-bends 23 (at the bottom in the drawing) is
arranged side by side in the first region 11 and a second 5 group of the Ubends
23 (at the top in the drawing) is arranged side by side in the second
region 12. The U-bends 23 of the second group are formed in the connecting
element 30, and the tube sections 21 extend from the connecting element 30
in the second region 12 to the first region 11. The power input elements 52
10 may be designed as desired, for example rigid, and, with rod-shaped
sections, can pass through a wall of the reactor vessel 10.
[0061] Means for feeding an inerting gas into the reactor vessel are denoted as a
whole by 50. As illustrated by arrows 53 (only partially denoted accordingly), the
15 inerting gas is fed into the reactor vessel 10 in particular via wall openings,
nozzles, or the like in one or more walls of the reactor vessel 10. In order to
provide and feed the inerting gas, suitable gas feed means are provided, which
are also illustrated here in a highly simplified manner, and which comprise, for
example, one or more gas tanks 51 and corresponding lines 52.
20
[0062] Figure 3 schematically illustrates a reactor, which is overall denoted
by 200, for carrying out a chemical reaction according to a development of
the present invention.
25 [0063] In the reactor 200, the tube sections – here in contrast denoted by 22 – in
each case comprise a tube section 22 consisting of a plurality of reaction tubes
20, wherein the tube sections 22 are arranged side by side in the reactor vessel
10 in a fluidically unconnected manner and are in each case connected to feed
sections 24 and extraction sections 25. For the remaining elements, reference is
30 expressly made to the above explanations relating to the preceding figures.
19
[0064] In turn, the use of a connecting element 30 within the framework of the
present invention is optional, albeit advantageous in particular when using a
polyphase alternating current heater. Here as well, power input elements 42 are
illustrated in a highly simplified manner. The feeding of the inerting gas according
to the arrows 53 takes place here as substantially explained 5 above. The power
input elements 42 can have a sleeve-like region 43, which is attached thereto and
placed in the first region 11 around the reaction tubes 20 or the tube sections.
[0065] Figures 4 to 8 show partial views of reactors according to embodiments
10 of the present invention in a further simplified illustration, wherein a chimney
60 is also illustrated in each case. The gas feed means 50 for feeding the
inerting gas are not shown, nor are the means 40 for electrical heating. The
reaction tube 20 is illustrated with U-bends according to Figure 2, but can also
be designed in any other form, for example according to Figure 3. A feeding of
15 inerting gas is indicated only at one location with an arrow 53.
[0066] As illustrated in Figure 4 with an arrow 54, false air can pass into the
reactor vessel 10 via one or more false air inlets. In the embodiment
illustrated here, the reactor vessel 10 has a permanently open discharge
20 orifice 61 connected to the chimney 60. The inerting gas feed and the high
temperatures in the reactor vessel 10 in relation to an end 63 of the chimney
60 result in a flow illustrated by arrows 64. In the reactor vessel, the high
temperatures lead to a static pressure pBox, which is below the atmospheric
pressure pAtm in the adjacent surroundings when the inerting gas feed is
25 carried out in an adapted manner. In other words, the amount of purge gas
is not selected to be too large here. With a very large amount of purge gas,
the pressure loss in the chimney 60 would lead to the internal pressure in the
reactor vessel 10 approaching or even exceeding the external pressure.
30 [0067] In this embodiment with negative pressure in the reactor vessel, this
amount prevents a return flow of ambient air into the reactor vessel 10 from
occurring; low false air entries due to insufficient sealing are also
20
compensated. The inerting gas supply into the reactor vessel 10 can in
particular be regulated via an oxygen measurement 65 in the chimney 60, so
that the oxygen content can be kept constant during operation.
[0068] In contrast to the embodiment according to Figure 5 4, the reactor vessel
10 according to Figure 5 is operated at a superatmospheric pressure level,
wherein inerting gas is continuously fed into the reactor vessel 10. The
reactor vessel 10 has a discharge orifice 62, for example in the form of a
bursting disk, which is set up to open above a preset pressure level.
10
[0069] In this alternative embodiment with pressurized operation, the inerting gas
supply compensates low gas leakages into the atmosphere, which are illustrated
here by an arrow 55. In this case, the purge quantity can be regulated via a
pressure measurement in the reactor vessel 10. For continuous inerting gas
15 purging, a correspondingly dimensioned outlet opening can be provided at a safe
location (in the region of the chimney 60 or at another not easily accessible and
non-hazardous location), so that a stream 66 from the reactor vessel 10 results.
[0070] As in the embodiment according to Figure 5, the reactor vessel 10
20 according to Figure 6 is operated at a superatmospheric pressure level. Here
as well, the reactor vessel 10 has a discharge orifice 62, for example in the
form of a bursting disk, which is set up to open above a preset pressure level.
However, a continuous throughflow of inerting gas is not provided, so that the
stream 66 does not form in this embodiment.
25
[0071] In this alternative embodiment with pressurized operation, a purging for
initial inertization is carried out, for example, only during operation preparation.
During the further operation, only the equalization quantity of inerting gas for
the leakage flows from the reactor vessel to the atmosphere is added
30 continuously or in intervals. In this embodiment, there is thus no permanently
open outlet for inerting gas to the atmosphere during normal operation.
21
[0072] In the embodiments according to Figures 4 to 6, operation of the
reactor with hydrocarbons is advantageously only released when a required
oxygen content is undershot.
[0073] In the embodiments according to Figures 5 4 and 5 with continuous
purging, the oxygen content is preferably measured in the discharge of the
purge gas downstream of the reactor vessel 10 (e.g., in the chimney 60 or
another discharge line). Additionally or alternatively, the oxygen content can
also be measured by means of suitable measuring methods (e.g., tunable
10 diode laser, zirconium oxide probes, GC paramagnet) at one or more locations
in the region of the reactor vessel 10. In the embodiment according to Figure
6, the oxygen content can be measured analogously in a purge gas discharge
line optionally used for the initial inertization and/or in the reactor vessel 10
itself. In addition, according to the embodiments according to Figures 5 and 6,
15 the pressure within the reactor vessel can be continuously measured and
monitored, in order to detect impermissible inerting gas loss early.
[0074] As indicated in more detailed drawings below, the chimney 60 in all
previously illustrated embodiments can have structural elements (so-called
20 velocity seals/confusor) in particular in the region of the chimney wall in order
to avoid air return flows (e.g., due to free convection flows) back to the reactor
vessel 20.
[0075] Figure 7 schematically illustrates a reactor for carrying out a chemical
25 reaction according to an embodiment of the invention in an extension with
respect to the illustration according to the preceding figures, wherein elements
already explained above are in part not illustrated again. For further
explanation, reference is made in particular to the above Figure 4.
30 [0076] As illustrated here, in the region of the chimney outlet 63, ignition devices
or pilot burners 68 can additionally be installed in order to at least partially
prevent the escape of uncombusted hydrocarbons into the atmosphere in the
22
event of a disaster. As further illustrated, the inerting gas can be fed into the
reactor vessel 10 at different sides. A wall of the reactor vessel 10 and wall
passages of fastenings or power input devices, which can each advantageously
be designed to be gas-tight, are denoted by 15. I and O denote a feed of process
gas and a removal of the process gas from the 5 reaction tube 20.
[0077] Figure 8 schematically illustrates a reactor for carrying out a chemical
reaction according to an embodiment of the invention in an extension to the
representation according to Figure 7 or a variant thereof. Components
10 already explained with respect to Figure 7 are partially not again provided
with reference signs here.
[0078] As illustrated here, the chimney 60 can have a suitable insulation 69 in
a region adjoining the reactor vessel 10. The chimney 70 can have a height h
15 of, for example, 20 to 50 meters above ground. A so-called velocity seal 66
may be provided in the chimney 60.
[0079] Figure 9 schematically illustrates the principles of chimney dimensioning
according to an embodiment of the present invention in the form of a diagram,
20 in which an oxygen content in percent is plotted on the abscissa and a reactionrelated
volume increase rate in m3/s is plotted on the ordinate. A graph 601
represents the relationship already explained above with reference to the table.
A dashed line 602 denotes values required for a maximum pressure increase of
20 mbar in the case of a chimney diameter of 500 mm; a dashed line 603
25 denotes corresponding values in the case of a chimney diameter of 900 mm.

I/We Claim:
1. A reactor (100, 200) for carrying out a chemical reaction, which has a
reactor vessel (10), one or more reaction tubes (20), and means (40) for the
electrical heating of the one or more reaction tubes 5 (20), wherein the reaction
tubes (20) are guided through the reactor (100, 200) with at least one U-bend
or run through it without U-bends, characterized in that the reactor vessel(10)
has one or more discharge orifices (61, 62) that are permanently open or are
set up to open above a preset pressure level, and in that gas feed means (50)
10 are provided which are set up to feed an inerting gas into the reactor vessel
(10), and in that means are provided that are set up to prevent reaction
operation if an oxygen content and/or pressure and/or hydrocarbon content
measured in the reactor vessel (10) and/or in a discharge line downstream of
the reactor vessel exceeds a respective preset value.
15
2. The reactor (100, 200) according to claim 1, which is set up to carry
out the chemical reaction at a temperature level of more than 500°C, in
particular of 700°C to 1000°C.
20 3. The reactor (100, 200) according to claim 1 or 2, wherein the one or
more discharge orifices (61) are permanently open.
4. The reactor (100, 200) according to claim 1 or 2, wherein the one or
more discharge orifices (62) are closed below the preset pressure level and
25 are set up to open temporarily or permanently when the preset pressure level
is reached.
5. The reactor (100, 200) according to one of the preceding claims,
wherein the gas feed means (50) are set up to continuously feed the inerting
30 gas into the reactor vessel (10).
24
6. The reactor (100, 200) according to one of the preceding claims,
wherein the gas feed means (50) are set up to supply the inerting gas to the
reactor vessel (10) once or periodically.
7. The reactor (100, 200) according to claim 5 3, wherein the reactor
vessel (10) is set up for operation at a subatmospheric pressure level and
has means for forming a gas flow from the reactor vessel (10).
8. The reactor (100, 200) according to claim 4, wherein the reactor
10 vessel (10) is set up for operation at a supercritical pressure level.
9. The reactor (100, 200) according to one of the preceding claims,
wherein the gas feed means (50) are set up to provide as the inerting gas a
gas or a gas mixture which has nitrogen, carbon dioxide, and/or argon in a
15 respectively superatmospheric content.
10. The reactor (100, 200) according to one of the preceding claims
wherein the one or more discharge orifices (61, 62) are connected to one or
more chimneys (60).
20
11. The reactor (100, 200) according to claim 10, wherein the gas feed
means (50) are set up to adjust a maximum oxygen content in the reaction
vessel (10) on the basis of a dimensioning of the chimney(s) (60).
25 12. The reactor (100, 200) according to one of the preceding claims,
wherein the gas feed means (50) are set up to regulate an amount of inerting
gas on the basis of an oxygen measurement.
13. A method for carrying out a chemical reaction, with which a reactor (100,
30 200) is used, which has a reactor vessel (10), one or more reaction tubes (20),
and means (40) for the electrical heating of the one or more reaction tubes (20),
wherein the reaction tubes (20) are guided through the reactor (100, 200) with at
25
least one U-bend or run through it without U-bends, characterized in that the
reactor vessel (10) used is a reactor vessel (10) which has one or more discharge
orifices (61, 62) which are permanently open or are set up to open above a preset
pressure level, and an inerting gas is fed into the reactor vessel (10) by using gas
feed means (50), and in that means are provided that are 5 set up to prevent
reaction operation if an oxygen content and/or a pressure and/or a hydrocarbon
content measured in the reactor vessel (10) and/or in a discharge line
downstream of the reactor vessel exceeds a respective preset value.